What is Left Bundle Branch Block?
Having a Left bundle branch block (LBBB) means the normal flow of electrical signals in your heart is partially blocked. This blockage can show up on a heart test called an electrocardiogram (ECG). While LBBB is commonly linked with heart diseases caused by heart muscle damage, strain, or enlargement, it can also be found in people without any health issues. Just having LBBB isn’t something to be worried about, nor does it directly affect your future health.
However, LBBB could be a serious concern in certain situations, especially for those experiencing acute chest pain, fainting (syncope), or a certain type of heart failure known as heart failure with reduced ejection fraction (HFrEF), meaning the heart can’t pump out as much blood as it should. A sudden onset of LBBB along with these symptoms could be a sign of disease and might indicate a heart attack.
New emergence of LBBB in some situations is considered equivalent to having an ST-segment elevation, a pattern that usually suggests a heart attack on an ECG, especially in patients with chest pain. Although traditionally, specific parts (the QRS and ST segments) of the ECG are hard to understand with LBBB, new guidelines called Sgarbossa criteria have been developed as a tool for making sense of these ECGs despite the difficulty.
What Causes Left Bundle Branch Block?
When heart tissue expands, it can lead to issues with electrical signals transferring between heart muscles. This same rule applies to the left bundle, a part of your heart’s natural pacemaker system. The main cause of an issue known as Left Bundle Branch Block (LBBB) is a condition called dilated cardiomyopathy.
Dilated cardiomyopathy is a disease that results in the enlargement of the left side of your heart, causing the tiny fibres essential for heart conduction, known as Purkinje fibers, to stretch and separate.
The reasons for the development of dilated cardiomyopathy are varied, including reduced blood supply (ischemic), infections, valve-related issues, infiltration of abnormal substances, and inflammation. However, the most common cause is reduced blood supply to the heart muscle.
Risk Factors and Frequency for Left Bundle Branch Block
Left bundle branch block (LBBB) is a condition that only affects about 0.06% to 0.1% of people in general. However, it is much more common in patients with heart failure, affecting approximately one-third of these individuals. The worse the left ventricular failure – a type of heart failure – becomes, the more likely it is for someone to have LBBB.
Signs and Symptoms of Left Bundle Branch Block
Left bundle branch block, often abbreviated as LBBB, doesn’t usually cause any physical symptoms. The only way it can typically be identified is through a specific pattern seen on an electrocardiogram (EKG), which is a type of heart test.
Testing for Left Bundle Branch Block
Left bundle branch block, often abbreviated as LBBB, is typically identified through an electrocardiogram (ECG), which is a medical test that measures the electrical activity of your heart. The American College of Cardiology (ACC) and American Heart Association (AHA) have set standards for diagnosing LBBB:
1. The rhythm of your heart must come from above the ventricles (the lower chambers of your heart). This means that the heartbeat is started from the atria (the upper chambers of the heart) or the AV node (the part of your heart that transmits signals between the atria and ventricles).
2. The QRS duration, which marks one full heartbeat on the ECG, needs to be longer than 120 milliseconds. This indicates that the electrical signals are moving slower than usual through your heart.
3. On ECG lead V1 (one specific view of the heart’s electrical activity), you should either have a QS wave (a certain pattern on the ECG) or a small r wave followed by a large S wave.
4. On ECG lead V6 (another specific view of the heart’s electrical activity), there should be a notched R wave, which shows a specific part of the heartbeat, and there should not be a Q wave (another specific part of the heartbeat).
Treatment Options for Left Bundle Branch Block
Left Bundle Branch Block (LBBB) isn’t something that is typically treated directly. This condition is usually permanent and often requires addressing any underlying health issues that may have contributed to its development. However, there is an exception for people suffering from heart failure, specifically a type called Heart Failure with Reduced Ejection Fraction (HFref), who also experience regular heart rhythms (sinus rhythm) accompanied by LBBB.
In these cases, the American College of Cardiology (ACC) and the American Heart Association (AHA) suggest that a therapy known as cardiac resynchronization could be beneficial, especially if the heart’s electrical signals (known as QRS wave) take longer than usual (over 150 milliseconds) to travel. Cardiac resynchronization, in combination with the correct medical therapy, can even help reduce the risk of death by up to 37% for these individuals.
Cardiac resynchronization therapy (CRT) may be a consideration for people who don’t have regular heart rhythms, like those with atrial fibrillation, and for those whose QRS waves take a slightly shorter time (120 to 149 milliseconds) to travel. However, this recommendation isn’t as strong.
It’s worth noting that CRT doesn’t clear the LBBB condition. Instead, it uses a bi-ventricular pacemaker to stimulate both the left and right ventricles (chambers) of the heart at the same time. This process bypasses the heart’s electrical system, thus ensuring the heart beats more effectively.
What else can Left Bundle Branch Block be?
When doctors are diagnosing a left bundle branch block (LBBB), there are other conditions that might show similar symptoms and could be confused for an LBBB. Some of these include:
- Intra-ventricular conduction delay: This can cause similar results on an ECG test, but usually does not include an R wave in V6.
- A paced rhythm: This can often be mistaken for LBBB, but it often does not have an R wave in V6 and you usually notice pacer spikes.
- Incomplete LBBB: If the LBBB pattern has a QRS duration less than 120 ms, it is referred to as an incomplete LBBB.
- Ventricular rhythm (run of PVCs) without super-ventricular stimulation: This might look very similar to a left bundle branch block and in certain rare situations, it may be impossible to distinguish from LBBB.
What to expect with Left Bundle Branch Block
In healthy people, Left Bundle Branch Block (LBBB), which is a condition that disrupts the heart’s natural rhythm, doesn’t usually pose any specific or additional risk. The death risk related to LBBB is only 1.3 times that of someone without this condition. However, for patients newly diagnosed with LBBB, the death risk increases to more than ten times the normal rate.
People especially at risk are those with chest pain and newly diagnosed LBBB, which should be considered as serious as ST-segment elevation, a significant sign of a heart attack. For heart failure patients, having LBBB can result in increased heart-related complications and a higher mortality rate.
However, according to recent research, if we exclude other factors contributing to the health outcomes, the impact of LBBB is much less severe. This is probably because LBBB is often a result of a condition called “dilated cardiomyopathy” rather than the cause that progresses the disease itself.
Because LBBB might be an early sign of complete atrioventricular block, a severe form of heart rhythm disorder, patients with this condition are not permitted to pilot aircraft in the United States and the United Kingdom. This relation is substantiated by epidemiological data. Therefore, if patients with LBBB have symptoms like fainting or a feeling of fainting, they are advised to undergo testing procedures like ECG and Holter Monitor, which can track the heart’s activity over time.
